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  <title>返回 exp(number) - 1，甚至当 number 的值接近零也能计算出准确结果</title>
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  <div id="layout-content"><div id="function.expm1" class="refentry">
   <div class="refnamediv">
    <h1 class="refname">expm1</h1>
    <p class="verinfo">(PHP 4 &gt;= 4.1.0, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">expm1</span> &mdash; <span class="dc-title">
     返回 exp(number) - 1，甚至当 number 的值接近零也能计算出准确结果
    </span></p>

   </div>
 <div class="refsect1 description" id="refsect1-function.expm1-description">
  <h3 class="title">说明</h3>
     <div class="methodsynopsis dc-description">
      <span class="methodname"><strong>expm1</strong></span>
    ( <span class="methodparam"><span class="type">float</span> <code class="parameter">$arg</code></span>
      ) : <span class="type">float</span></div>

    <p class="para rdfs-comment">
     <span class="function"><strong>expm1()</strong></span> 返回 &#039;exp(<code class="parameter">number</code>) - 1&#039;，甚至当
     <code class="parameter">number</code> 的值接近零也能计算出准确结果。但是当两个数值趋近于相等的时候，
     &#039;exp (<code class="parameter">number</code>) - 1&#039; 就会变得不太准确。
    </p>
   </div>

 <div class="refsect1 parameters" id="refsect1-function.expm1-parameters">
  <h3 class="title">参数</h3>
  <p class="para">
   <dl>

    
     <dt>
<code class="parameter">arg</code></dt>

     <dd>

      <p class="para">
       要处理的参数
      </p>
     </dd>

    
   </dl>

  </p>
 </div>

 <div class="refsect1 returnvalues" id="refsect1-function.expm1-returnvalues">
  <h3 class="title">返回值</h3>
  <p class="para">
   &#039;e&#039; to the power of <code class="parameter">arg</code> minus one
  </p>
 </div>

 <div class="refsect1 changelog" id="refsect1-function.expm1-changelog">
  <h3 class="title">更新日志</h3>
  <p class="para">
   <table class="doctable informaltable">
    
     <thead>
      <tr>
       <th>版本</th>
       <th>说明</th>
      </tr>

     </thead>

     <tbody class="tbody">
      <tr>
       <td>5.3.0</td>
       <td>
         此函数在所有平台上均可用
       </td>
      </tr>

     </tbody>
    
   </table>

  </p>
 </div>

 <div class="refsect1 seealso" id="refsect1-function.expm1-seealso">
  <h3 class="title">参见</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member"><span class="function"><a href="log1p.html" class="function" rel="rdfs-seeAlso">log1p()</a> - 返回 log(1 + number)，甚至当 number 的值接近零也能计算出准确结果</span></li>
    <li class="member"><span class="function"><a href="exp.html" class="function" rel="rdfs-seeAlso">exp()</a> - 计算 e 的指数</span></li>
   </ul>
  </p>
 </div>

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